1. Field of the Invention
The present invention relates to a protecting film for FPD (Flat Panel Display) such as PDP (Plasma Display Panel), PALC (Plasma Addressed Liquid Crystal Display), and the like, a method of producing the same, and FPD using the same.
2. Description of the Related Art
As a method of forming a protecting film at low cost with excellent productivity as compared with a method of forming a FPD protecting film using a vacuum process such as an electron beam deposition process, a sputtering process, an ion plating process, or the like, various methods have been proposed. These proposed methods use a wet process such as a screen printing process, a spin coating process, a spray coating process, or the like using paste or a coating solution containing a MgO powder, a Mg(OH)2 powder, a mixture of MgO powder and Mg(OH)2 powder, or a rare earth oxide powder (for example, Japanese Unexamined Patent Publication Nos. 3-67437, 7-220640, 7-147136, 7-335134, 8-111177, 8-111178, 8-212917, 6-325696, 8-167381, 8-264125, 9-12940, 9-12976, 8-96718, etc.).
As this type of protecting film, a secondary electron emitting material for a plasma display panel is disclosed, which comprises a pair of discharge maintaining electrodes, a dielectric layer and a protecting layer, which are laminated on a back glass substrate, a fluorescent layer formed on the rear side of a front glass substrate, and an inert gas sealed between both substrates and emitting ultraviolet rays by discharge, the protecting layer being composed of a secondary electron emitting material such as fluorinated MgO (Japanese Unexamined Patent Publication No. 7-201280). In this secondary electron emitting material, oxygen of MgO which constitutes the protecting layer is partially replaced by fluorine. Namely, the oxygen atoms of a lattice which forms a MgO ion crystal are partially replaced by fluorine atoms to form fluorinated MgO represented by the formula MgO1-X-YFY (wherein 0 less than X less than 1 and 0 less than y less than 1).
This secondary electron emitting material for a plasma display panel uses fluorinated MgO represented by MgO1-X-YFY as the protecting layer, and thus forms localized levels by valence control, thereby decreasing the break-down voltage. As a result, it is possible to form a high-definition panel, and obtain a protecting film stable with the passage of time.
On the other hand, as a PDP protecting film which is directly exposed to a discharge space and is thus a key material playing the most important role in discharge characteristics, a MgO film having the high secondary electron emitting ability, and excellent sputtering performance, light transmission, and insulating property is conventionally used.
However, the MgO film is easily degenerated due to reaction with CO2 and H2O when exposed to air during the process. Therefore, it is known that in order to obtain the original characteristics of MgO, degassing evacuation must be carried out under vacuum and heating for a long time after panel sealing (for example, Latest Plasma Display Manufacturing Technology, edited by Sato, Press Journal, p. 118-123 and p. 291-295 (1997)). This is because impurity gases of H2O, H2, O2, CO, CO2, N2, and the like adversely affect discharge characteristics of PDP and a constituent material of a panel, and particularly, contamination with CO2 deteriorates panel characteristics to an unrecoverable level.
Therefore, in order to prevent degeneration of MgO, it has been proposed to coat the surface of MgO with another material having low moisture permeability (Japanese Unexamined Patent Publication No. 10-149767, and W, T, Lee et al; xe2x80x9cLaF3 coated MgO protecting layer in AC-Plasma Display Panelsxe2x80x9d, IDW""98, P. 72-75).
The above Japanese Unexamined Patent Publication No. 10-149767 discloses a method of manufacturing PDP comprising forming a protecting film, forming a temporary protecting film with low moisture permeability on the protecting film, and then removing the temporary protecting film. In this method, the surface of the protecting film is protected by the temporary protecting film during manufacture of PDP, preventing the formation of a degenerated layer on the surface of the protecting film. As a result, a protecting film having good discharge characteristics can be obtained, and pyrolysis of the degenerated layer of the protecting film is made unnecessary.
The above document of W. T. Lee et al proposes that LaF3 coating having low moisture permeability on a MgO protecting film can suppress degeneration of the MgO protecting film, and realize a higher degree of secondary-electron emitting property and a lower degree of discharge property.
However, in the conventional method of forming a protecting film disclosed in each of the above publications, a MgO powder, a Mg(OH)2 powder, a MgO powder obtained by burning a mixture of MgO powder and Mg(OH)2 powder, or a rare earth oxide powder comprises fine particles and thus has a large surface area, thereby causing the probability that the surfaces relatively readily react with carbon dioxide and moisture in air to form a carbonate and hydroxide. There is thus a problem in that carbon dioxide and moisture are released to the discharge space during discharge of PDP to deteriorate discharge characteristics.
In addition, the secondary-electron emitting material for a plasma display panel disclosed in Japanese Unexamined Patent Publication No. 7-201280 comprises a protecting layer composed of fluorinated MgO represented by MgO1-X-YFY, and thus has a problem in that since a difference between the thermal expansion coefficients of the protecting layer and a substrate (dielectric layer) is relatively large, the protecting layer and the substrate (dielectric layer) have low adhesion and matching therebetween, and poor electric insulation as compared with the use of a MgO film as a protecting layer.
Furthermore, the PDP manufacturing method disclosed in Japanese Unexamined Patent Publication No. 10-149767 and the document of W. T. Lee et al is difficult to match the temporary protecting film and the protecting film in formation of the temporary protecting film, and thus causes cracks in the temporary protecting film or peeling of the temporary protecting film, thereby causing the insufficient effect of preventing degeneration of the protecting film by the temporary protecting film. A possible method of improving this is to coat a thick temporary protecting film on a protecting film. However, this method has the problem of producing large amounts of impurities (decomposition products of the temporary protecting film) in removal of the temporary protecting film.
Furthermore, the document of W. T. Lee et al discloses that LaF3 is coated to 5 to 90 nm on MgO. However, such a two-layer structure has a problem in that the break-down voltage is rapidly changed when the LaF3 upper layer film is removed by sputtering, thereby failing to obtain a sufficient life time.
Accordingly, a first object of the present invention is to provide a FPD protecting film and a method of producing the same which is capable of preventing deterioration in adhesion and matching with a substrate (dielectric layer), and preventing deterioration in electric insulation.
A second object of the present invention is to provide a FPD protecting film and a method of producing the same which is capable of inhibiting or suppressing reaction of MgO or the like in a film body, a film or the protecting film with CO2 gas and H2O gas in air to prevent or suppress degeneration of MgO to MgCO3, Mg(OH)2, etc. harmful to FPD, i.e., capable of improving the environment resistance of the film body, the film or the protecting film.
A third object of the present invention is to provide a FPD protecting film and a method of producing the same which is capable of preventing or suppressing the formation of a carbonate (MgCO3 or the like), a hydroxide (Mg(OH)2), etc. of MgO before the formation of a fluoride layer on the surface of a film body to shorten the time of the vacuum evacuation heating step or omit the vacuum evacuation heating step during manufacture of FPD.
A fourth object of the present invention is to provide a FPD protecting film and a method of producing the same which permits the relatively easy formation of a fluoride layer with a high secondary-electron emitting ability on the surface of a film body or the surfaces of MgO powder which constitutes the film.
A fifth object of the present invention is to provide FPD using a protecting film which is capable of significantly decreasing the number of production steps.
A sixth object of the present invention is to provide a method of producing a FPD protecting film, which is capable of improving matching between a fluoride layer and a protecting film to prevent the occurrence of cracks in the fluoride layer and peeling of the fluoride layer in the FPD manufacturing process, and improve the effect of preventing degeneration of the protecting film by the fluoride layer.
A seventh object of the present invention is to provide a FPD protecting film and a method of producing the same which permits the removal of a fluoride layer after assembly of FPD to improve the discharge characteristics.
In accordance with the present invention, as shown in FIGS. 1 and 2, a FPD protecting film comprises a film body 14a formed on a substrate 13 and made of any of MgO, CaO, SrO, BaO, alkali earth compound oxides, rare earth oxides, and compound oxides of alkali earth oxides and rare earth oxides; and a fluoride layer 14b formed on the surface of the film body 14a. 
In the FPD protecting film the surface of the film body 14a is coated with the fluoride layer 14b, and thus MgO or the like in the film body 14a little reacts with CO2 gas and H2O gas in air even when the protecting film 14 is exposed to air for a long time in the process for manufacturing FPD 10 (refer to FIG. 2). As a result, MgO or the like in the film body 14a is little degenerated to MgCO3 and Mg(OH)2 which possibly deteriorate the function of the FPD 10.
Since the film body 14a having substantially the same thermal expansion coefficient as the substrate 13 is bonded to the substrate 13, the protecting film 14 is not separated from the substrate 13 due to a heat cycle, thereby causing high adhesion and matching between the protecting film 14 and the substrate 13.
In accordance with the present invention, as shown in FIGS. 3 and 4, a FPD protecting film comprises a film body 34a formed on a substrate 13 and made of any one of MgO, CaO, SrO, BaO, alkali earth compound oxides, rare earth oxides, and compound oxides of alkali earth oxides and rare earth oxides, wherein the film body 34a is formed by using a fluoride layer-coated powder of any one of MgO, CaO, SrO, BaO, alkali earth compound oxides, rare earth oxides, and compound oxides of alkali earth oxides and rare earth oxides.
In the FPD protecting film the surfaces of MgO powder particles or the like are coated with fluoride layers, and thus MgO or the like in the film body 34a little reacts with CO2 gas and H2O gas in air even when the protecting film 34 is exposed to air in the manufacturing process (refer to FIG. 4). As a result, MgO or the like in the film body 34a is little degenerated to MgCO3, Mg(OH)2, etc. having the probability of deteriorating the function of FPD 10. Since the fluoride layers coated on the surfaces of MgO powder or the like are very thin, the mechanical characteristics of the MgO powder or the like are substantially the same as a MgO powder or the like with no fluoride layer coated on the surfaces thereof.
The fluoride layer 14b is preferably represented by MOXFY (M is Mg, Ca, Sr, Ba, an alkali earth complex metal, a rare earth metal, or a complex metal of an alkali earth metal and a rare earth metal, 0xe2x89xa6X less than 2, and 0 less than Yxe2x89xa64).
The fluoride layer 14b is preferably obtained by reaction of a gaseous fluorinating agent with any one of MgO, CaO, SrO, BaO, alkali earth compound oxides, rare earth oxides, and compound oxides of alkali earth oxides and rare earth oxides.
Furthermore, as the gaseous fluorinating agent, any one of fluorine gas, hydrogen fluoride gas, BF3, SbF5 and SF4, particularly, fluorine gas or hydrogen fluoride gas, is preferably used. The thickness of the fluoride layer is preferably set in the range of 0.1 to 1000 nm.
In accordance with the present invention, a method of producing a FPD protecting film comprises forming a film body 14a on a substrate 13 by using any one of MgO, CaO, SrO, BaO, alkali earth compound oxides, rare earth oxides, and compound oxides of alkali earth oxides and rare earth oxides; and treating the surface of the film body with a gaseous fluorinating agent to form a fluoride layer 14b on the surface of the film body 14a, as shown in FIGS. 1 and 2.
In the method of producing a FPD protecting film, MgO or the like in the film body 14a is little degenerated to MgCO3 and Mg(OH)2 which are harmful to the function of the FPD 10 (refer to FIG. 2), thereby shortening the time of the subsequent degassing step for removing MgCO3 and Mg(OH)2 or omitting the subsequent degassing step.
In accordance with the present invention, a method comprises forming a film body 14a on a substrate 13 in a vacuum, and treating the surface of the film body 14a with a gaseous fluorinating agent in a vacuum or an inert gas atmosphere without exposing the film body 14a to air to form a fluoride layer 14b on the surface of the film body 14a, as shown in FIGS. 1 and 2.
In the method of producing a FPD protecting film, after the film body 14a is formed on the surface of the substrate 13, the film body 14a is not exposed to air before the fluoride layer 14b is formed on the surface of the film body 14a, thereby preventing or suppressing the production of carbonate (MgCO3, or the like) and hydroxide (Mg(OH)2, or the like) of MgO, which are harmful to the FPD, on the surface of the film body 14a. 
In accordance with the present invention, a method comprises forming a film body 14a on a substrate 13 in a vacuum, burning the film body 14a in air after exposing the film body 14a to air to activate the film body 14a, and treating the surface of the film body 14a with a gaseous fluorinating agent to form a fluoride layer 14b on the surface of the film body 14a, as shown in FIGS. 1 and 2.
In the method of producing a FPD protecting film, after the film body 14a is formed on the surface of the substrate 13, the film body 14a is exposed to air and burned in air to be activated. Therefore, even when carbonate (MgCO3, or the like) and hydroxide (Mg(OH)2, or the like) of MgO, which are harmful to the FPD, are formed on the surface of the film body 14a, the carbonate (MgCO3, or the like) and hydroxide (Mg(OH)2, or the like) of MgO are removed as CO2, and H2O by burning in air. In this state, the fluoride layer 14b is formed on the surface of the film body 14a to protect the surface of the film body 14a by the fluoride layer 14b, thereby preventing and suppressing the formation of carbonate (MgCO3, or the like) and hydroxide (Mg(OH)2, or the like) of MgO.
In accordance with the present invention, a method further comprises activating the film body 14a before, during or after the substrate 13 on which the film body 14a and the fluoride layer 14b are formed is assembled into a panel.
In the method of producing a FPD protecting film, since the film body 14a is activated by burning after the fluoride layer 14b is formed on the surface of the film body 14a, even when hydroxide (Mg(OH)2, or the like) of MgO or the like is formed a little on the film body 14a, the hydroxide can be removed as H2O, thereby decreasing the rate of recontamination of the film body 14a with atmospheric moisture.
In accordance with the present invention, a method of producing a FPD protecting film comprises treating, with a gaseous fluorinating agent, the surfaces of a powder of any one of MgO, CaO, SrO, BaO, alkali earth compound oxides, rare earth oxides, and compound oxides of alkali earth oxides and rare earth oxides to coat fluoride layers on the powder surfaces of any one of MgO, CaO, SrO, BaO, alkali earth compound oxides, rare earth oxides, and compound oxides of alkali earth oxides and rare earth oxides; mixing a binder, a solvent and the fluoride layer-coated powder of any one of MgO, CaO, SrO, BaO, alkali earth compound oxides, rare earth oxides, and compound oxides of alkali earth oxides and rare earth oxides to prepare paste or a dispersion for a film; and forming a film body 34a on the surface of a substrate 13 by using the paste or dispersion for a film, as shown in FIGS. 3 and 4.
In the method of producing a FPD protecting film, since MgO or the like in the film body 34a is little degenerated to MgCO3, Mg(OH)2, etc. harmful to the function of the FPD 10 (refer to FIG. 4), it is possible to shorten the time of the subsequent degassing step for removing the MgCO3, Mg(OH)2, etc., or omitting the subsequent degassing step, thereby decreasing the manufacturing cost of the FPD 10.
In the method according to the present invention, the film body 14a made of any one of MgO, CaO, SrO, BaO, alkali earth compound oxides, rare earth oxides, and compound oxides of alkali earth oxides and rare earth oxides, or the powder of any one of MgO, CaO, SrO, BaO, alkali earth compound oxides, rare earth oxides, and compound oxides of alkali earth oxides and rare earth oxides is preferably surface-treated with the gaseous fluorinating agent under pressure of 1 to 760 Torr.
In the method, as the gaseous fluorinating agent, any one of fluorine gas, hydrogen fluoride gas, BF3, SbF5, and SF4, particularly fluorine gas or hydrogen fluoride gas, is preferably used.
A powder of any one of MgO, CaO, SrO, BaO, alkali earth compound oxides, rare earth oxides, and compound oxides of alkali earth oxides and rare earth oxides is coated with a fluoride layer in order to form a FPD protecting film 34.
The thickness of the fluoride layer coated on the powder is preferably 0.1 to 1000 nm.
The paste for a film is prepared by mixing a binder, a solvent, and the fluoride layer-coated powder of any one of MgO, CaO, SrO, BaO, alkali earth compound oxides, rare earth oxides, and compound oxides of alkali earth oxides and rare earth oxides.
The dispersion for a film is prepared by mixing a binder, a solvent, and the fluoride layer-coated powder of any one of MgO, CaO, SrO, BaO, alkali earth compound oxides, rare earth oxides, and compound oxides of alkali earth oxides and rare earth oxides.
The use of the paste or dispersion for a film containing the fluoride layer-coated powder permits easy formation of a film body.
The FPD uses a protecting film.
The FPD of the present invention permits a significant decrease in number of steps for manufacturing FPD, and manufacture at low cost.
In accordance with the present invention, a method of producing a FPD protecting film comprises forming, on the surface of a substrate 13, a protecting film 54 made of any one of alkali earth metal oxides, alkali earth metal compound oxides, rare earth metal oxides, and compound oxides of alkali earth metals and rare earth metals treating the surface of the protecting film 54 with a gaseous fluorinating agent to form a fluoride layer 55 on the surface of the protecting film 54; and then removing the fluoride layer 55 after FPD is assembled by using the substrate 13, as shown in FIG. 5.
In the method of producing a FPD protecting film, the protecting film 54 is reacted directly with the gaseous fluorinating agent to form the fluoride layer 55 on the surface of the protecting film 54, thereby coating the surface of the protecting film 54 with the fluoride layer 55. Therefore, even when the protecting film 54 is exposed to air for a long time during the process for manufacturing the FPD 10, the protecting film 54 little reacts with CO2 gas and water vapor in air. As a result, the protecting film 54 is little degenerated to a carbonate, a hydroxide, etc., of an alkali earth metal oxide or the like, which have the probability of deteriorating the function of the FPD 10. On the other hand, it is possible to prevent the occurrence of cracking in the fluoride layer 55 and separation thereof because of good matching between the fluoride layer 55 and the protecting film 54, thereby improving the degeneration protecting effect of the protecting film 54.
The fluoride layer is preferably represented by MOXFY (wherein M is Mg, Ca, Sr, Ba, and alkali earth complex metal, a rare earth metal, or a complex metal of an alkali earth metal and a rare earth metal, 0xe2x89xa6X less than 2, and 0 less than Yxe2x89xa64). The fluoride layer is preferably obtained by reaction of the gaseous fluorinating agent with any one of alkali earth metal oxides, alkali earth metal compound oxides, rare earth metal oxides, and compound oxides of alkali earth metals and rare earth metals.
Furthermore, as the gaseous fluorinating agent, any one of fluorine gas, hydrogen fluoride gas, BF3, SbF5 and SF4, particularly fluorine gas or hydrogen fluoride gas, is preferably used. The thickness of the fluoride layer is preferably set in the range of 0.1 to 1000 nm.
In accordance with the present invention, the FPD protecting film 54 is produced as shown in FIG. 5.
The FPD 10 uses the protecting film 54 as shown in FIG. 5(d).
In the FPD protecting film 54, the fluoride layer 55 is removed after assembly of the FPD 10, thereby improving discharge characteristics of the FPD 10.